The present invention is directed to a non-commutated electric linear motor and to an automobile door lock mechanism driven by a non-commutated linear motor. More particularly, the present invention is directed to a linear motor assembled from a series of spaced coils formed either on an armature or maintained in a series of stacked cups serving as the windings of a linear motor. The linear motor is of sufficient size to have the appropriate force and length of stroke to actuate an automobile door lock mechanism.
In many currently utilized electric door lock mechanisms, an electric motor having an electric motor armature, gears and a mechanical drive train is connected to a door lock mechanism. A typical system may include a latching bolt to secure the door to the frame of the automobile, an electric switch located inside the door for locking or unlocking the bolt, a manually-displaceable handle inside of the door for unlatching the door, a manually movable button, slide or similar device for locking and unlocking a latching bolt in the door, and, on the exterior of the door, a handle for latching and unlatching the door and a key opening for receipt of a key for unlocking and locking the latching bolts. The key receiving mechanism may be designed to either manually unlock the latching bolts or to energize a motor to unlock the latching bolts. At this point in time most entry locks utilize the motion imparted by turning the key to unlock the latching bolts.
One of the problems identified with this type of system is that the manual effort required to turn the key to unlock the latching bolt may be significant. If the ambient temperature is low, or if there is insufficient lubrication, or a key is particularly weak, in any of the above events, the force required to manually unlock the latching bolt may be such that the key is either twisted or broken in the process and entry of the car is denied.
It has been determined that one of the mechanisms acting to create the difficulty in manually unlocking the latching bolts is that the electric motor, gears, and remainder of the electric drive train to the door lock actuator are mechanically coupled thereto, and in order to manually displace the latching bolt, it is necessary to "back drive" the gear train and the electric motor as the latching bolt is displaced. Hence, additional force on the key is required and additional work is necessary to accomplish the rotation of the motor armature and the displacement of the gear train or the actuator.
The herein-described non-commutated linear motor avoids the necessity of "back driving" a gear train and a rotating motor since it is a non-commutated linear motor and displacement of the latching bolt may simply result in displacement of the linear sliding armature having but a minimal force required to effect such displacement.
Solenoids have been used in some specific car designs to power automobile door locks. However, solenoids are inherently inefficient, for the same force output are sized larger than linear motors, and typically solenoids generate a greater amount of force at the end of the travel stroke than at the beginning. Solenoids are also noisy, costly and create large induced currents in the automobile wiring system when turned on and off. These induced currents may create electrical noise problems with onboard computers and other smart devices. Because of these disadvantages the use of solenoids has all but disappeared from automotive applications.
A linear motor, on the other hand, when appropriately designed may be of compact size and be designed to accommodate the necessary travel stroke. Additionally, the linear motor may simply be designed to provide approximately constant force over its entire stroke length, thereby generating a larger amount of initial force such that the size of the entire motor may be minimized.
Additionally, by proper design of the linear motor, a compact package may be provided which is sized to fit appropriately within an automobile door. By using a motor length which may simply be adjusted by adding or deleting windings, the appropriate stroke length and other operating characteristics may be readily obtained or changed. Furthermore, a motor generating sufficient force while meeting the physical constraints of the automotive application, may also be designed which has a maximum current draw less than the maximum allowed current draw on the wire specified within the door by an automotive manufacturer.